Time-domain optical medical images show great promise as a technique for imaging breast tissue, as well as the brain and other body parts. The objective is to analyze at least a part of the temporal point spread function (TPSF) of an injected light pulse as it is diffused in the tissue, and the information extracted from the TPSF is used in constructing a medically useful image.
Two fundamental techniques are known by which the TPSF can be obtained: time domain and frequency domain. In time domain, a high intensity, short duration pulse is injected and the diffused light is detected within a much longer time frame than the pulse, but nonetheless requiring high-speed detection equipment. In frequency domain, light is modulated in amplitude at a range of frequencies from the kHz range to about 0.5 GHz. The light injected is modulated but essentially continuous, and the information collected is the amplitude and the phase difference of the light at the detector. Thus, lower intensities are required, and the demands of very short, high intensity injection pulse generation and high-speed detection are avoided. The acquisition of the data requires the two parameters of amplitude and phase shift to be recorded for a large number of modulation frequencies within the dynamic range provided. The TPSF could be calculated by inverse Fourier transform, however, the image is typically generated using the frequency domain data.
In optical imaging of human breast tissue, the breast is immobilized by stabilizing plates of the optical head. Although the light injected is not harmful, prolonged imaging time is uncomfortable for patients, particularly in the case of female breast imaging in which the breast is typically secured between support members or plates, and is typically immersed in a bath or surrounded by a coupling medium contained in a bag. While optical imaging promises a safer and potentially a more medically useful technique, imaging time and related patient discomfort remains a problem in providing a competitively superior technique.
To maintain the objective of acquiring the best quality images that the technology will permit, a minimum acquisition time is required. This acquisition time required to generate quality medical images determines the cost efficiency of the imaging equipment. Thus a reduction in imaging time will result in greater throughput.